Scientific name: Wonambi naracoortensis Scientific classification:
Family: Madtsoiidae When did it become extinct? This snake became extinct around 40,000 years ago. Where did it live? This snake was only found in Australia.
The snakes are a very odd group of reptiles. Sinuous and legless, they have evolved some amazing ways of catching their food and protecting themselves. Although these limbless reptiles are endlessly fascinating, their origins are nothing short of a mystery. It is thought that their closest relatives are the monitor lizards, and although snake fossils are quite common, they can be hard to study, so we can only guess at how and why these remarkable reptiles evolved from lizard ancestors with functional limbs to the serpents we know today.
The evolutionary history of the snakes may be sketchy, but some answers have been discovered in the home of animal anomalies: Australia. In various cave sites in Australia, paleontologists have found the bones of a long-dead animal that belonged to a very ancient group of snakes, all of which are now extinct. This group, the Madtsoiidae, survived for around 90 million years, from the middle of the Cretaceous to the Pleistocene. They were once found in Australia, South America, Africa, Madagascar, and Europe, but they slowly died out, until
Australia was their last refuge, and Wonambi was one of the last of their number. The bones of this animal from the Victoria fossil caves show that it was a large snake, perhaps as much as 6 m long, which is comparable to some of the largest pythons and boa constrictors alive today.
Like the living giant snakes, Wonambi was probably nonvenomous, instead relying on ambush tactics and its muscular body to catch and suffocate prey using constriction. Constriction is actually a very effective means of subduing prey and is used by a large number of snakes, not only by the large boas, pythons, and anacondas. Wonambi probably loitered around watering holes and other places that attracted its prey. If a suitable victim came within striking distance of the Wonambi's hiding place, the snake launched a lightning-fast lunge, snagging the prey with its sharp, curved teeth. In the blink of an eye, Wonambi threw coil after coil of its long body around the struggling victim. The embrace of Wonambi must have been an inescapable one as the reptile tightened its grip, slowly suffocating the victim with crushing force. When the prey was dead, Wonambi relaxed its grip and set about swallowing the still warm body. The snakes we know today have a fantastically flexible skull and lower jawbone that makes it possible for them to swallow large animals. Large pythons and the anaconda can inch their head over their prey until the whole body is engulfed. Wonambi was a primitive snake, and it lacked the highly flexible skull of the modern snakes; therefore it was probably limited to smaller prey such as the many species of smaller wallaby that still inhabit Australia. The larger marsupials, many of which are now extinct, were probably too big for Wonambi to handle, but any animal visiting a water hole in ancient Australia was probably always wary of being caught in a Wonambi ambush.
As the living giant snakes can catch and eat huge prey animals, they can go for many months between meals. They rest and digest their prey for several days or weeks, and their very efficient metabolism enables them to make the very most of all the food they eat. As Wonambi didn't have the head or jaws for large prey, it may have needed to eat more frequently than the living constrictors.
Wonambi was the last of a long line of primitive snakes and one of many such giants that once slithered their way around Australia. They seem to have died out with the rest of the Australian megafauna around 40,000 years ago, but as new evidence comes to light, this date may change significantly. Humans may have known these snakes, and it is possible that human activities, such as bushfires, led to their demise. Australia, like the rest of the world, has been through some massive climatic changes in the past 2 million years or so, and perhaps the demise of these snakes coincided with the disappearance of the lush vegetation that once shrouded the Australian continent, leaving the arid landscape we know today. Water holes and other habitats favored by Wonambi disappeared, and its prey grew increasingly difficult to find. Confronted by this changing world and the pressure of human hunting, the Wonambi and the other primitive snakes eventually disappeared.
♦ For a long time, it was assumed that the snakes descended from a burrowing ancestor that took to a life underground and lost its limbs. This may be partially true as the eyes of snakes are unique among the vertebrates, with many features that are not seen in any fish, amphibian, reptile, bird, or mammal. Some scientists have argued that this is because the ancestors of snakes were subterranean animals that completely lost their eyes as well as their limbs. As they moved back onto the surface to fill vacant niches, their eyes reevolved into the unique structure we see today.
♦ Snake fossils can be numerous, especially the very durable vertebrae. There are even several skeletons of extinct snakes that are more or less complete. Some of the primitive extinct snakes even had hind legs.
♦ The vestiges of these hind legs can be seen in the most primitive of the living snakes: the large constrictors (boas, pythons, and the anaconda). In some of these species, the male has a pair of tiny spurs on the back end of his body, which are used during mating. These spurs are the last vestige of the snake's hind limbs. If you were to cut one of these snakes open, you would see the pelvic bones and the vestigial leg bones.
♦ The Wonambi takes its name from one of the "rainbow snakes," the mythical serpents in the creation stories of the Aboriginal people. Perhaps these myths are based on reality?
Further Reading: Scanlon, J. D., and M.S.Y. Lee. "The Pleistocene Serpent Wonambi and the Early Evolution of Snakes." Nature 403 (2000): 416-20; Scanlon, J. D., and M.S.Y. Lee. "The Serpent Dreamtime." Nature Australia, summer 2001; Brown, S. P., and R. T. Wells. "A Middle Pleistocene Vertebrate Fossil Assemblage from Cathedral Cave, Naracoorte, South Australia." Transactions of the Royal Society of South Australia 124 (2000): 91-104.
^ Extinction Insight: A Hole in the Desert—The Nullarbor Plain Caves
Immediately north of the Great Australian Bight, the large open bay on the south coast of Australia, lies the Nullarbor Plain, the largest single outcrop of limestone in the world, with an area of around 200,000 km2. The limestone of this plain was laid down millions of years ago in a shallow sea, but geological activity forced the huge slab into its present position. This flat and treeless semiarid plain is far from inviting, but beneath its surface are treasures.
Limestone is dissolved slowly by rainwater, and over millions of years, any large area of this rock soon becomes riddled with caves and tunnels. This is exactly what has happened to the Nullarbor Plain, and its flat surface belies a network of caverns and tunnels, only a tiny proportion of which have been explored. In May 2002, a group of cavers found a sinkhole on the surface of the Nullarbor Plain—a sinkhole appears when the roof of a limestone cavity is dissolved, leaving a short pipe into the cavern beneath. They decided to explore the sinkhole and lowered themselves through the 11-m pipe and into the cavern below. It was a further 20 m to the floor of the cavern, and when they shined their head torches on the rocks around their feet, they were met with a site that no human had ever before seen. Around them, littering the floor of the cavern, were numerous skeletons. Some of the bones were semiconcealed by sediment, while others were lodged between rocks and boulders. Obviously, these were not the remains of creatures that had died recently, and realizing the importance of their find, the cavers alerted the authorities. Following the discovery, a team of paleontologists and geologists visited the site and lowered themselves into the caves. It soon became clear to them that this was a very important find, probably one of the most significant paleontological discoveries on Australian soil. What lay before them was a more or less complete record of the animals that once stalked the Nullarbor Plain above their heads. The remains of the animals were perfectly preserved, but they were fragile, and before any of the bones were removed, they were painted with a special strengthening compound.
In total, 69 species of vertebrate were identified from the caves, many of which survive in Australia to this day. Twenty-one of the identified animals did not survive the Pleistocene and are known only from bones. Of the 23 species of kangaroo identified from the remains in the cave, no fewer than 8 were new species, which goes to show just how diverse Australia's large animal fauna once was. One of the most interesting of these extinct kangaroos was a small species with bony protrusions above its eyes, like small horns. Exactly what these were for is a mystery, but paleontologists have speculated that they protected the animal's eyes from the spines of its food plants. Interestingly, two of the extinct kangaroos from the cave were tree-dwelling species, similar to the surviving rainforest kangaroos of New Guinea. The site also yielded no fewer than 11 complete skeletons of the marsupial lion, an animal that was only previously known from a handful of skeletons. The largest animal in the assemblage was the extinct giant wombat, Phascolonus gigas, which, at 200 kg, goes to show that the sinkhole was quite some pitfall trap.
All of the amazing animals the scientists discovered fell through the opening of the sinkhole and ended up on the chamber floor some 30 m beneath the surface. Not many of the remains were found
The Nullarbor Plain Caves—A caver is shown descending through a narrow sinkhole into one of the Nullarbor Plain caves, which yielded an unparalleled haul of ancient animal remains in an incredible state of preservation. (Clay Bryce)
directly beneath the opening in the chamber ceiling, so it seems the fall was not fatal. Badly injured on the floor of the cave, the hapless animals crawled away into the darkness and died a slow death from their injuries and a lack of food and water. The scientists were finding the animals in the same positions in which they had died thousands of years previously, but when exactly had these animals fallen into the cave? Analysis of the sediments in the cave show that the cavern was first opened to the surface about 790,000 years ago. Over millennia, natural processes had sealed the sinkhole on numerous occasions, only for heavy rain and geological activity to open it again. It seems that the opening closed for the last time about 195,000 years ago, so what's preserved at the bottom of this cave is a 600,000-year record of the animals that once lived in this part of Australia.
These caves show not only how diverse the Australian megafauna was, but also what the landscape and climate were like. Today, the Nullarbor Plain is a relatively lifeless landscape, and the flora of the area is dominated by saltbush (Atriplex sp.) and bluebush (Maireana aphylla) scrub. Thousands of years ago, this was not the case, as trees and other plants, many of which have since disappeared, were common. Instead of the arid steppe we find today, the Nullarbor Plain was probably a mosaic of woodland and scrub, with plants that bore palatable leaves and fleshy fruits. The fact that arboreal kangaroos have been recovered from the caves is proof that these plains supported large trees thousands of years ago. Interestingly, the climate of the ancient Nullarbor Plain was no different to what we see today, with average annual rainfall of around 180 mm. The drying of Australia's climate is often cited as the cause of the extinction of the megafauna this huge island once supported. The Nullarbor caves suggest otherwise. The animals and plants of Western Australia were well suited to arid conditions, and the disappearance of the bizarre beasts from this arid plain may be due to wildfires (natural or caused by humans) that wiped out many of the plant species, leaving the impoverished landscape we see today. With their food dwindling, the herbivores of the Nullarbor died out, closely followed by the predators and scavengers.
Further Reading: Prideaux, G. J., J. A. Long, L. K. Ayliffe, J. C. Hellstrom, B. Pillans, W. E. Boles, M. N. Hutchinson, R. G. Roberts, M. L. Cupper, L. J. Arnolds, P. D. Devine, and N. M. Warburton. "An Arid-Adapted Middle Pleistocene Vertebrate Fauna from South-Central Australia." Nature 445 (2007): 422-25.
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